In certain systems for erosion control, a bed of interlocking concrete blocks is laid on a filter blanket of bonded fibrous material which serves to prevent erosion of the underlying material whilst permitting the free passage of water. A characteristic of the filter blanket is a very high coefficient of friction, and this makes the blocks, which individually may weigh as much as 90 pounds, difficult to man-handle and position accurately on the mat. An object of the invention is to provide a mechanical aid to the laying and accurate positioning of such blocks, not only on such filter blankets, but also on beds of material such as sand or gravel which might be disrupted if the blocks were shifted over their surfaces.
It has been proposed to facilitate the laying of paving bricks and blocks by mechanical devices in which the bricks or blocks are laid on an apron over which they may readily be moved into position, and when several courses of bricks or blocks have been laid, a pusher bar is actuated to hold the blocks against displacement whilst the apron is partially withdrawn from beneath the blocks so that the latter are gently transferred onto a bed or blanket of material onto which they are to be laid. Such apparatus is described in U.S. Pat. No. 1,527,983 to Lundstrom and U.S. Pat. No. 1,571,386 to Straight.
The apparatus disclosed in these patents is relatively sophisticated and is intended for laying a level pavement on roadways in which the curvature will usually be slight and the camber, if any, will be relatively constant. In erosion control applications, the layer of blocks may have to follow complex contours on steep slopes, and relatively sharp bends along winding water courses, as well as abrupt changes of gradient. Moreover, a degree of flexibility in the interlocking system of blocks is required. All this requires some degree of adjustment in the relative alignment of the blocks so as to provide an interlocking layer of blocks which will follow the contours of the ground to be protected whilst maintaining a desired orientation of the blocks. These requirements cannot be met by the known apparatus, which relies on the existence of a prepared roadway to keep it on a desired alignment and is designed to produce an entirely uniform pavement.